1. Field of the Invention
The present invention relates in general to the field of transmissions, including, for example, Ford transmission models 5R55W, 5R55S, and 5R55N. More particularly, the present invention relates to a design and modification of OEM parts for these transmissions that, when used, repairs functionality to the intermediate and overdrive servos due to worn bores in the transmission housing.
2. Background of the Invention
Transmission servos, which are sometimes referred to as pistons, are used to activate different gear ranges within the transmission, along with other functions. Solenoids within the transmission open and close ports that apply and remove pressure to the servos allowing shifting, for instance, from 1st gear to the intermediate range gears (e.g., 2nd, 3rd, 4th) and/or from 4th gear to the overdrive (e.g., 5th Gear, or above).
During normal operation, a solenoid activates to allow hydraulic fluid flow and pressure to the piston side opposite the direction you want the servo to move. The transmission is designed such that the pistons' surface area is sufficiently large to receive sufficient force against the pistons, provided by the fluid pressure delivered by the transmission pump, and applying that force onto the bands of the gear range being activated via the servo rod.
In the designs of the transmissions specified, the servo consists of a hardened shaft that is attached to the piston. This hardened shaft passes through an aluminum bore machined into the transmission housing. A port is located within the bore that, when opened by the solenoid, passes fluid through a cross bore in the rod to a center bore in the rod and up to the front side of the piston.
The theory in the original design is that, through the passage of fluid to the front side of the piston, pressure builds up between the servo cap/cover and the piston. This is accomplished by seals around the diameter of the piston and around the diameter of the servo cap/cover. These are the only two places where seals are originally designed into the system.
Due to the forces acting on the servo rod, i.e., the repeated activation and deactivation, as well as the reaction forces to the coupling to the transmission bands and other forces, over time, the hardened steel shaft wears on the aluminum bore and causes leakage to the back side of the piston. This leakage causes back pressure on the servo rod and opposite pressure applied to the piston head, as well as leakage into the transmission reservoir. Both of these results in a reduced amount of fluid pressure available to the front side of the piston which in turn reduces the available force to the bands and causes the gear ranges that are being activated to not work properly. The bands slip when there is not enough force, which causes unsafe driving conditions or, at a minimum, severely decreased performance.
The only means of fixing this, up to the proposed invention, was to remove the transmission and do a partial disassembly of the transmission. Then the servos would need to be removed, and the bores for the rods would need to be machined out and sleeves made of a more wear-resistant material pressed into the bored out bores. This method requires a high level of skill and a large set of expensive equipment to perform. If this procedure is performed by a mechanic or dealer, it ends up running into the thousands of dollars. Also, given the complicated level of skills required, it severely limits the ability for someone with reasonable mechanical ability to perform the work themselves. This invention provides a very cost-effective fix that can be performed by most people with minimal mechanical abilities. It is also the most cost-effective fix in the market to date that is available to mechanics, dealers, and repair shops.